A conventional chip-in-glass type VFD device includes an integrated circuit chip for driving a display unit in a vacuum glass envelope thereof. The integrated circuit chip is connected to external terminals by conductor patterns to be supplied with an electric power from external power supply.
According to the conventional VFD device, however, there is a disadvantage in that potential change, which is caused by resistances of the external terminals themselves and connecting points of the external terminals and the conductor patterns, occurs at pads of the integrated circuit chip. When the integrated circuit chip has two inputs for power supplying, one of which is for low potential power supply (for instance, ground level) and other is for high potential power supply (for instance, +V.sub.C), potential of the pad for low potential power supply becomes higher than that of the external terminal for low potential power supply. On the other hand, the high potential power supply becomes lower than that of the external terminal for high potential power supply. That is, the potentials of the ground level and +V.sub.C are changed to be -V.sub.D and V.sub.C -V.sub.D, respectively, where V.sub.D is the potential change. As a result, the integrated circuit chip may not operate stably or may not produce expected characteristics.